Did you notice that the graph is rising faster than never before on the right and that it is already warmer than in the middle ages? Temperature changes because of many factors, and something else might have caused the high temperature in the middle ages or the little ice age (maybe natural variaton of C02 concentration?). In fact, I don't know exactly what caused them, and I am humble enough not to ump into any conclusions about that, whithout even informing myself further about this.

It is a fact that it is proven that gases like CO2 act as greenhouse gases, which contribute to increasing temperatures. And we know that CO2 concentration went up and temperatures went up.

And if we act now, and we are wrong, we didn't cause any harm (except that it was WORK, omg...), but if we don't act now, but global warming is a fact, we doom ourselves.

(And what a coincidence that both global warming deniers here are from the USA. It would be an even bigger coincidence if they both the Republicans )